In conventional deposition apparatuses, the deposition process is performed only on one side of a substrate at a time. Another side is usually maintained in contact with a supporting surface, such as a roller or a flat plate, which may be used as a reference during deposition and/or to provide temperature control to the substrate. In some embodiments, the substrate is a web. A web may exert some pressure onto the supporting surface created by web tension and/or web weight. When two sided deposition is needed, a web is typically processed twice. Deposition is performed on one side first. The web is then rewound back through the same deposition station or fed through another deposition station to deposit on the other second side. As a result, processing time or equipment costs are doubled.
Further, during the second side deposition, the web with material already deposited on the first side is again exposed to process conditions, which may involve high temperature and/or reactive processing gases. The first side, which contacts the supporting surface under these conditions, often experiences substantial compressive and/or shear forces exerted by the supporting surface. Such approach may not be suitable for depositing fragile materials. For example, silicon nanowires may easily break when compressed or sheared at a temperature above 350° C. A first side deposited materials (e.g., an active electrode layer) may collapse or break during second side deposition and become unsuitable for use in batteries or other applications.
Methods and apparatuses are needed to deposit materials on both sides of a web in efficient ways while keeping materials deposited on both sides intact.